The invention is based on patent application Nos. 11-332034 Pat., 11-330763 Pat., 11-330869 Pat., 11-332008 Pat. and 11-332013 Pat. filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal element, and particularly a liquid crystal element of a layered type including a plurality of liquid crystal layers.
2. Description of the Background Art
A liquid crystal element is basically formed of a pair of substrates and a liquid crystal layer held between the substrates.
A drive voltage is applied to the liquid crystal layer to control orientation of liquid crystal molecules so that incoming light is modulated to perform intended display or the like.
For monochrome display of images, the element usually employs a single layer of liquid crystal. For display in multiple colors, a plurality of liquid crystal layers each capable of display in an intended color are layered to form the liquid crystal element of the layered type.
A liquid crystal element of a reflection type, which utilizes selective reflection of the liquid crystal exhibiting a cholesteric phase, may be used for full color display. This liquid crystal element has a layered structure including, for example, three liquid crystal layers, which are layered together, and perform display in blue, green and red, respectively.
For good image display, the liquid crystal element or the layered type liquid crystal element is required to achieve high-contrast and bright display and others.
For achieving such a requirement, various proposals have been made. However, it is still required or desired to improve the contrast and others of the liquid crystal elements, and particularly the liquid crystal elements of the layered type which have been proposed.
For example, light passing though the respective liquid crystal layers may cause multiple reflection. Also, the light passing through the respective liquid crystal layers may unnecessarily scatter. The influence of the multiple reflection and/or the unnecessary scattering may lower the contrast in the image display.
In the liquid crystal element of the layered type, which includes the plurality of liquid crystal elements adhered and layered together, an adhesive material (adhesive layer) for adhering the neighboring liquid crystal elements together may scatter the light, resulting in low contrast.
If the liquid crystal element uses a resin film substrate, interference of light may occur in a wavelength range from red light to infrared rays and/or unnecessary scattering of light may occur. These may lower the brightness and contrast in image display. In the structure using the resin film substrate, the thickness thereof may be minimized so that light modulation characteristics such as display characteristics may not be impaired. However, such a thin substrate may cause disadvantages such as bending of the liquid crystal element and/or breakage of an electrode. These disadvantages are particularly remarkable in the liquid crystal element of the layered type.
Further, a certain kind of liquid crystal element uses an orientation film for controlling orientation of the liquid crystal within the liquid crystal layer. The orientation film is provided, for example, for inclining the liquid crystal molecules at a predetermined angle with respect to an orientation film surface (substrate surface). The angle at which the orientation film inclines the liquid crystal molecules with respect to the substrate surface is referred to as a xe2x80x9cpretilt anglexe2x80x9d. The orientation film is utilized also for the purpose of orientating the liquid crystal molecules in a predetermined direction. By effecting rubbing on the orientation film, the liquid crystal molecules can be orientated in the rubbing direction. The orientation film described above is arranged between the liquid crystal layer and the substrate, and is in contact with the liquid crystal in the liquid crystal layer.
It can be considered that the orientation film described above affects the contrast of the liquid crystal element, and particularly the liquid crystal element of the layered type.
An object of the invention is to provide a liquid crystal element as well as a liquid crystal element of a layered type, which have improved contrast.
Another object of the invention is to provide a liquid crystal element of a layered type, which can suppress an influence by multiple reflection and unnecessary scattering, and can have improved contrast.
Still another object of the invention is to provide a liquid crystal element of a layered type, which can perform bright image display.
Yet another object of the invention is to provide a liquid crystal element of a layered type, which can perform bright image display with a low voltage drive (low power consumption).
Further another object of the invention is to provide a liquid crystal element and a liquid crystal element of a layered type, which can perform bright image display with good contrast.
A further object of the invention is to provide a liquid crystal element of a layered type, which can achieve bright image display with a low voltage drive (low power consumption) as well as with good contrast.
A further object of the invention is to provide a liquid crystal element of a layered type, which can perform improved white-display.
A further object of the invention is to provide a liquid crystal element of a layered type, which can perform image display with a good color balance.
A further object of the invention is to provide a liquid crystal element of a layered type which includes a plurality of liquid crystal elements layered and adhered together, and particularly the liquid crystal element which can suppress scattering of light due to an adhesive layer adhering the neighboring liquid crystal elements, and thereby can achieve good contrast.
A further object of the invention is to provide a liquid crystal element and a liquid crystal element of a layered type, which can achieve high contrast, and can suppress problems such as bending of the liquid crystal element and breakage of an electrode.
A further object of the invention is to provide a liquid crystal element and a liquid crystal element of a layered type, which can ensure good electrical conductivity of electrodes.
A further object of the invention is to provide a liquid crystal element of a layered type, which is provided with a plurality of liquid crystal layers layered together as well as orientation films for the respective liquid crystal layers, and can achieve good contrast.
First, the invention provides the following first to third liquid crystal elements.
(1) First Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between electrode formation surfaces of a pair of substrates each provided with an electrode, an insulating film is disposed between each of the liquid crystal layers and the electrode on at least one of the paired substrates holding the layer, and at least two liquid crystal layers of the plurality of liquid crystal layers have the insulating films opposed to the liquid crystal layers and being different in refractive index from each other, respectively.
(2) Second Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between electrode formation surfaces of a pair of substrates each provided with an electrode, an insulating film is disposed between each of the liquid crystal layers and the electrode on at least one of the paired substrates holding the layer, and at least two liquid crystal layers of the plurality of liquid crystal layers have the insulating films opposed to the liquid crystal layers and being different in kind from each other, respectively.
(3) Third Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between electrode formation surfaces of a pair of substrates each provided with an electrode, an insulating film is disposed between each of the liquid crystal layers and the electrode on at least one of the paired substrates holding the layer, and the insulating film opposed to the liquid crystal layer at an outermost position on an element observation side has a refractive index larger than a refractive index of the insulating film opposed to the neighboring liquid crystal layer.
The invention also provides the following fourth liquid crystal element.
(4) Fourth Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein at least one of the liquid crystal layers has a thickness different from those of the other liquid crystal layers, and the liquid crystal layer at an outermost position on a side remote from an element observation side has a thickness equal to or larger than that of any one of the liquid crystal layers on the element observation side, and contains a liquid crystal material having a refractive index anisotropy value equal to or larger than that of any one of liquid crystal materials contained in the liquid crystal layers on the element observation side.
The invention also provides the following fifth liquid crystal element.
(5) Fifth Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal elements layered and adhered together, wherein each of the liquid crystal elements has a pair of substrates and a liquid crystal layer held between the substrates, and an adhesive layer disposed between the neighboring substrates of the neighboring liquid crystal elements for adhering the neighboring liquid crystal elements has a thickness not exceeding a quarter of a thickness of at least one of the neighboring substrates.
According to the study by the inventors, the following has been found in connection with a liquid crystal element having a liquid crystal layer and a pair of resin films each provided with an electrode and holding the liquid crystal layer therebetween. In this liquid crystal element, at least one of the opposite electrodes, which is located on the observation side, may have a relatively large thickness for increasing the influence by the film characteristics of this electrode, and thereby the interference of light in the wavelength range from the red light to the infrared rays is reduced in each liquid crystal layer. Further, a good electrical conductivity can be ensured in the electrode. Moreover, the electrode may have a thickness of a predetermined value or less, whereby the bending of the substrate is prevented while keeping the foregoing characteristics, which facilitates manufacturing of the element, and prevents breakage of an electrode. Other effects can also be achieved. For example, a thin resin film substrate can be used without difficulty, which contributes to improvement of the display characteristics.
By increasing the refractive index of the resin film substrate, the difference in refractive index between the substrate and the electrode formed thereon decreases so that unnecessary scattering of light passing therethrough is suppressed.
Based on the knowledge described above, the invention provides the following sixth to eighth liquid crystal elements.
(6) Sixth Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between a pair of resin films each carrying an electrode, and at least the electrode on an element observation side has a thickness from 1200 xc3x85 to 1500 xc3x85 and a surface resistance of 200 ohm/square (200xcexa9/xe2x96xa1) or less.
(7) Seventh Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between a pair of resin films each carrying an electrode, and at least the resin film substrate on an element observation side has a thickness from 50 xcexcm to 200 xcexcm and a refractive index of 1.58 or more, and carries the electrode having a thickness from 1200 xc3x85 to 1500 xc3x85 and a surface resistance of 200 ohm/square (200xcexa9/xe2x96xa1) or less.
(8) Eighth Liquid Crystal Element
A liquid crystal element, wherein a pair of resin film substrates each carrying an electrode hold a liquid crystal layer exhibiting a cholesteric phase therebetween, and at least the electrode formed on the substrate on an element observation side has a thickness from 1200 xc3x85 to 1500 xc3x85 and a surface resistance of 200 ohm/square (200xcexa9/xe2x96xa1) or less.
Further, the invention provides the following ninth liquid crystal element.
(9) Ninth Liquid Crystal Element
A liquid crystal element of a layered type including a plurality of liquid crystal layers, wherein each of the liquid crystal layers is held between a pair of substrates, an orientation film is disposed between each of the liquid crystal layers and at least one of the paired substrates holding the liquid crystal layer, the orientation film opposed to at least one of the liquid crystal layers has a pretilt angle different from those of the orientation films opposed to the other liquid crystal layers, the orientation film opposed to the liquid crystal layer disposed nearest to an element observation side has the pretilt angle equal to or larger than the pretilt angles of the orientation films opposed to the other liquid crystal layers.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.